Flexible packaging films provide manufacturers with the ability to improve both the aesthetics and functional performance of packaging for both food and non-food items. With the development of stronger and tougher packaging materials which offer better puncture and tear resistance, the packages themselves have become increasingly more difficult to open. There have been a number of improvements in flexible packaging films over the years that have dealt with methods to initiate and control the opening of packages formed from various flexible packaging film combinations.
U.S. Pat. No. 3,608,815 to Bunch discloses films formed from cellophane laminated to an oriented material, i.e., polypropylene, polyethylene, or polystyrene. The opening aid consists of a rectangular linear pattern of punctures applied to the side edge region of a package. The control of the direction of opening is provided by the molecular orientation of the oriented material.
U.S. Pat. No. 4,834,245 to Ohga, et al. describe a flexible packaging laminate having a first outer layer of a polymeric resin with a molecular orientation in one direction, a second inner aluminum foil layer, a third outer layer of a polymeric resin with a molecular orientation in two directions. Two notches or cuts are made in close proximity on one side of the package to form a tab of film which helps initiate the tearing process. The tab further helps to direct the tearing in a direction parallel with the direction of orientation of the first outer layer which has a principal orientation in a uniaxial direction.
However, due to the enhanced durability and toughness of many packaging films today, maintaining the direction of tearing along a line parallel with the molecular orientation of the packaging film becomes a problem. In fact, the force required to tear the film is often greater than the molecular orientation relied on to control the direction of momentum. In many instances, the lack of control of the direction of tearing leads to uneven tearing of the package film which then results in premature spillage of the packaged contents.
U.S. Pat. No. 4,903,841 to Ohsima, et al. disclose a three-layered packaging film formed from biaxially oriented polyester, aluminum foil and biaxially oriented polypropylene laminate and packages made therefrom. The packages have a notch or cut made in the side heat sealed edge and two surface roughened lines one on each outer layer of the front and rear walls of the package. The surface roughened lines are parallel with the top portion of the package and extend from one side edge to the opposite side edge. To facilitate the tearing of the package, both surface roughened lines must be superimposed on each other and be aligned with the notch on the side edge.
However, it will be recognized to those skilled in the art, that keeping surface roughened lines in registration during the manufacturing process of multiple film packages is difficult without adding greater complexity to the manufacturing process and increased costs to production.
U.S. Pat. No. 5,613,779 to Niwa discloses packaging films having structures such as, for example, a first resin layer being biaxially oriented polyethylene terephthalate, a layer of an aluminum foil, and a second resin layer of non-oriented polypropylene. To guide to opening of the package, the outside surface of the package, which corresponds to the first resin layer of the laminate, is scored to form series of linear slits extending in a direction parallel with molecular orientation of the resin. Two notches are added to the package to initiate the tearing process.
However, the main disadvantage of forming slits to the outside surface is that it adversely affects the external appearance of the package, once the latter have been produced.
U.S. Pat. No. 6,427,420 to Olivieri, et al. describe a four-layered packaging laminate comprising a first layer of polyethylene terephthalate, a second layer of aluminum foil, a third layer of polyamide, and a fourth layer of polypropylene. Packages may be formed by making a transverse fold across a single rectangular sheet of laminate and heat sealing at least two or three edges together. These packages include at least one line of perforations made in the two inner most layers of the package and are produced using a laser beam in the form a succession of micro dots. These packages may also include a start-off-notch on one of the lateral edges if two lines of perforations are made in the package, however, the start-off-notch must be positioned between the lines of perforation for it to aid in opening of the package.
However, in such a package, there remains a problem because when a start-off-notch is used to initiate tearing of the film, at least two lines of perforation are required to control the direction of tearing of the film during the opening process. Forming two lines of perforation requires either two separate laser sources to create each line of perforation or a single laser source being divided into two beams. In either case, production costs are increased because of the purchase of additional lasers and/or the equipment needed to control a more complicated manufacturing process.
One or more of the aforementioned defects or drawbacks encountered in the prior art are substantially eliminated or ameliorated by embodiments of the present invention in one or more of the following aspects.
In one aspect, the present invention relates to a flexible packaging film comprising a first film layer having an internal and external surface in which the external surface further comprises a surface-roughened portion formed thereon; a second film layer comprising an adhesive; a third film layer comprising either a oxygen barrier material, a water vapor barrier material or both; and a fourth layer which has an internal and external surface wherein the external surface further comprises at least one score-line formed therein. Moreover, a flexible packaging film of the present invention may be easily torn apart manually when a surface-roughened portion on a first film layer and a score-line in a fourth film layer are configured so that they intersect an imaginary axis drawn between both first layer and fourth film layer and when the imaginary axis is perpendicular to the plane of the first film layer or the fourth film layer.
In another aspect, the present invention relates to a package formed from a flexible multilayer film having a tear initiation area which allows the package to be easily opened manually without any heavy manual force or cutting means.
In still another aspect, the present invention relates to a package formed from a flexible multilayer film having a controllable tear zone which affords directional control during the opening process of the package.